Migrate HIDE_NAVBAR_WINDOW to aconfig and rename is to enable_taskbar_navbar_unification

Bug: 309671494
Test: N/A
Change-Id: I5268027079aba44d1d49dc6b1da3cc699b98884a
diff --git a/libs/WindowManager/Shell/aconfig/multitasking.aconfig b/libs/WindowManager/Shell/aconfig/multitasking.aconfig
index 0e59e9a..29bdd5c 100644
--- a/libs/WindowManager/Shell/aconfig/multitasking.aconfig
+++ b/libs/WindowManager/Shell/aconfig/multitasking.aconfig
@@ -28,3 +28,10 @@
     description: "Enables invoking split contextually"
     bug: "276361926"
 }
+
+flag {
+    name: "enable_taskbar_navbar_unification"
+    namespace: "multitasking"
+    description: "Enables taskbar / navbar unification"
+    bug: "309671494"
+}